This invention relates generally to wind turbines, and more particularly, to wind turbines having rotor blades built in more than one piece and with load-reducing characteristics.
Recently, wind turbines have received increased attention as an environmentally safe and relatively inexpensive means of extracting energy from wind. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a drive train located within a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators, rotationally coupled to the rotor through a gearbox. The gearbox may be used to step up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid. Some turbines utilize generators that are directly coupled to the rotor without using a gearbox.
As the power generating capacity of wind turbines increases, the dimensions of their rotor blades and other components also increase. Furthermore, to maximize energy capture in the majority of wind regimes, it is beneficial to have as large a rotor diameter as possible for a particular generator rated capacity. At some point, however, practical transportation and logistics limits may be exceeded. Moreover, as physical size increases, inertial and aerodynamic loads that the structure must carry rise. These limitations lead to constraints on both energy production ratings and the rotor diameter for a particular rated capacity.